Vibrating screens are commonly used to sort, grade or classify particulate material, such as sand and aggregate.
A typical vibrating screen comprises a frame, typically defined by a pair of substantially parallel side walls interconnected by transversely extending bridging members, upon which is mounted a polyurethane screen deck having small openings or slots for water and/or undersize particles to pass through.
The frame is mounted on a chassis via resilient mountings and the frame, and thus the screen, is typically vibrated by means of a device including a pair of counter rotating rotors defining eccentric masses driven by one or more drive motors, to impart circular or reciprocating vibratory motion to the screen. In a grading screen, the screen deck is typically arranged at a predetermined slope and material to be graded is delivered onto an upper end of the screen, typically entrained in a flow of water, particularly if they material is also being washed. The screen is vibrated at high frequency to convey the material over the screen deck and to cause undersize material (and water if present) to pass through the openings in the screen deck, oversize material being discharged from a lower end of the deck onto a stockpile conveyor or into a collection bay or hopper.
It is known to provide a multi-deck screening assembly to produce a number of different grades of product. A plurality of screen decks, typically two or three decks, are typically arranged one above the other, and generally parallel to each other, each with a downward slope from an upper receiving end to a lower discharge end at which over-sized material (relative to the screen deck concerned) can be discharged. Material of a size in excess of the size of the screening apertures of each screen deck is discharged under gravity action from the lower end of the respective deck onto a respective stockpile conveyor, whereas under-sized material able to pass downwardly through the screening apertures of the respective screen deck falls under gravity onto the deck below, where the further screening action takes place, or into a collection region or sump in the case of the lowest deck. A triple deck screen assembly can grade feed material into four or more separate grades (particle size) of product.
A problem with existing triple deck screen assemblies is how to arrange each of the stockpile conveyors within the dimensional constraints of the chassis while enabling over-sized material from each deck to be delivered onto a respective stockpile conveyor. Typically a first stockpile conveyor extends laterally from a first side of the chassis, transverse to the screening decks, for conveying oversized material from a lower deck, a second stockpile conveyor extending laterally from a second side of the chassis, opposite the first side, for conveying oversized material from an intermediate deck, typically via a intervening delivery chute, and a third stockpile conveyor extends from an end of the chassis, substantially perpendicular to the first and second stockpile conveyors and aligned with a longitudinal axis of the chassis, for conveying oversized material from an upper deck, typically via a intervening delivery chute. This arrangement increases the overall length of the screening assembly and also restricts access to the discharge end of each deck. As such, one or more of the stockpile conveyors and/or delivery chutes typically require removal to provided access to the discharge ends of the decks.